1. Technical Field of the Invention
The present invention relates to a clock spring (which is called also "a cable reel" or "rotary connector") utilized for connecting members rotating relatively with each other by means of a cable, and more particularly to the structure of a clock spring in which a flexible flat cable (hereinafter referred to merely as "an FFC", when applicable) is prevented from being folded.
2. Description of the Related Art
FIG. 3 shows a conventional clock spring of reverse type. The clock spring 1 comprises a cylindrical outer casing 2, and a cylindrical inside rotator 3. Between the outer casing 2 and the inside rotor 3, a carrier 5 is movably provided, and an FFC 4 is accommodated. The FFC 4 is wound on the rotator 3. One end of the FFC 4 is led out through an outlet 3a, and then reversed by the reverse portion 5a of the carrier 5, while the other end is connected to the connector (not shown) of the outer casing 2.
When the rotator 3 is turned clockwise, the FFC 4 is rewound, so that it is wound on the inner cylindrical surface of the outer casing 2 while leaving from the reverse section 5a.
FIG. 4 shows another conventional structure in which idler rollers 7 are provided on a carrier 5. In the structure, a FFC 4 is reversed by a reverse roller 7a of the idler rollers 7.
In the clock spring shown in FIG. 3, when the FFC 4 is rewound and a reversed portion 4a thereof is left from the reverse portion 5a of the carrier 5 as indicated by a chain line, the reversed portion 4a is brought into slide contact with the surface 5b of the carrier 5 which is opposite to the reverse portion 5a, thus providing a slide friction. This slide friction makes it rather difficult for the FFC 4 to be fed out. If the rotor 3 is further turned under this condition, since the FFC 4 is not smoothly fed out, the FFC 4 is folded near the outlet 3a, which makes the circuit of the FFC 4 open.
In the clock spring having the reverse roller 7a as shown in FIG. 4, the aforementioned slide friction can be reduced at the time of operation of ordinary rewinding the FEC 4. However, in the case of the FFC 4 which has been wound tight (the counterclockwise turn of the rotator 3) is abruptly rewound (the clockwise turn of the rotator 3), the reversed portion 4a of the FFC 4 enters while being deformed outside of the reverse roller 7a as indicated by a chain line, so that it is rather difficult for the FFC 4 to be fed out, and accordingly the FFC 4 is liable to be folded near the outlet 3a.
As is apparent from the above description, the conventional clock spring suffers from problems that it may be damaged by the folding of the FFC 4, and is low in reliability and in durability.